A storage apparatus that is connected to a host computer via a network comprises a plurality of magnetic disks as storage devices for storing data, for example. The storage apparatus utilizes RAID (Redundant Arrays of Independent Disks) technology to render redundant the storage areas of the plurality of storage devices and construct a RAID group. In addition, the storage apparatus provides the host computer with storage areas from part of the RAID group and of the capacity required by the host computer, as logical volumes.
Furthermore, data duplicate removal technology is attracting attention for the purpose of suppressing the increased data volumes stored on the aforementioned magnetic disks and of raising data capacity efficiencies. Data duplicate removal technology is technology with which, if data that is newly written to a storage device, or so-called ‘write data’ has the same content as data already stored on a magnetic disk, duplicate data is not written to the magnetic disk. Verification of whether the write data has the same content as the data stored on the magnetic disk is typically performed using the data hash values (for example, PTL1).